JP5445970B2 - Magnetoresistive element and magnetic random access memory - Google Patents

Description

  The present invention relates to a magnetoresistive effect element and a magnetic random access memory. In particular, the present invention relates to a domain wall motion type magnetoresistive effect element and a magnetic random access memory.

  Magnetic Random Access Memory (MRAM) is expected as a non-volatile memory capable of high-speed operation and infinite rewriting, and has been actively developed. In the MRAM, a magnetic material is used as a storage element, and information is stored in correspondence with the magnetization direction of the magnetic material. Several methods have been proposed as a method for switching the magnetization of the magnetic material, but all of them are common in that current is used. For practical use of MRAM, it is very important how much the write current can be reduced. According to Non-Patent Document 1 below, the write current can be reduced to 0.5 mA or less, more preferably 0.2 mA or less. Reduction is required.

[Non-Patent Document 1] Sakimura, N. et al., “MRAM Cell Technology for
Over 500-MHz SoC, ”April 2007, IEEE Journal of Solid State Circuits, Vol. 42,
Issue 4, p830-838

  The most common method of writing information to the MRAM is to arrange a wiring for writing around the magnetic memory element, and to change the magnetization direction of the magnetic memory element by a magnetic field generated by passing a current through the wiring. It is a method of switching. Since this method uses magnetization reversal by a magnetic field, writing in 1 nanosecond or less is possible in principle, which is preferable for realizing a high-speed MRAM. However, the magnetic field for switching the magnetization of the magnetic material that has ensured thermal stability and disturbance magnetic field resistance is generally about several tens of Oe (Ehrstead). In order to generate such a magnetic field, about several mA is required. A current is required. In this case, the chip area is inevitably increased, and the power consumption required for writing increases, so that it is inferior in competitiveness compared to other random access memories. In addition to this, when the element is miniaturized, the write current further increases, which is not preferable in terms of scaling.

  In recent years, the following two methods have been proposed as means for solving such problems. The first is spin injection magnetization reversal. In this method, a laminated film composed of a first magnetic layer having reversible magnetization and a second magnetic layer electrically connected to and fixed in magnetization is formed. By utilizing the interaction between the spin-polarized conduction electrons and the localized electrons in the first magnetic layer when a current is passed between the second magnetic layer and the first magnetic layer, the first magnetic layer is used. Information is recorded by reversing the magnetization of the magnetic layer. Since spin injection magnetization reversal occurs at a certain current density or higher, the current required for writing is reduced as the element size is reduced. That is, it can be said that the spin injection magnetization reversal method is excellent in scaling. However, generally, an insulating layer is provided between the first magnetic layer and the second magnetic layer, and a relatively large current must be passed through the insulating layer at the time of writing. Sex is an issue. In addition, since the current path for writing and the current path for reading are the same, there is a concern about erroneous writing during reading. Thus, although spin transfer magnetization reversal is excellent in scaling, there are some barriers to practical use.

On the other hand, the magnetization reversal method using the current-induced domain wall motion phenomenon, which is the second method, can solve the above-described problems of spin injection magnetization reversal. An MRAM using the current-induced domain wall motion phenomenon is disclosed, for example, in Patent Document 1 below.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-191032 In general, an MRAM using a current-induced domain wall motion phenomenon is generally antiparallel to the first magnetic layer having reversible magnetization. It is fixed to become. In such a magnetization arrangement, a domain wall is introduced into the first magnetic layer. As reported in Non-Patent Document 2 below, when a current is passed in the direction penetrating the domain wall, the domain wall moves in the direction of the conduction electrons, so that a current is passed through the first magnetic layer. Writing becomes possible.

[Non-Patent Document 2] Yamaguchi, A. et al., “Real-Space Observation
of Current-Driven Domain Wall Motion in Submicron Magnetic Wires, ”Physical
Review Letters, Vol. 92, February 2004, number 7, p77205

  Since current-induced domain wall motion also occurs when the current density is higher than a certain current density, it can be said that there is scaling as in spin injection magnetization reversal. In addition to this, in the MRAM element using current-induced domain wall motion, the write current does not flow through the insulating layer, and the write current path and the read current path are different, so that the spin injection magnetization reversal can be mentioned. The above problem will be solved.

In Non-Patent Document 2, the current density required for current-induced domain wall movement requires about 1 × 10 ⁸ [A / cm ² ]. In this case, for example, when the width of the layer in which the domain wall motion occurs is 100 nm and the film thickness is 10 nm, the write current is 1 mA. This cannot satisfy the above-mentioned conditions concerning the write current. However, the following Non-Patent Document 3 reports that the write current can be reduced sufficiently by using a material having perpendicular magnetic anisotropy as a ferromagnetic layer in which current-induced domain wall motion occurs.

[Non-Patent Document 3] Fukami, S. et al., “Micromagnetic analysis of
current driven domain wall motion in nano-strips with perpendicular magnetic
anisotropy, ”52nd Annual Conference on Magnetism and Magnetic Materials,
Abstracts, January 2007, p352

  For this reason, when manufacturing MRAM using current-induced domain wall motion, it can be said that it is preferable to use a ferromagnetic material having perpendicular magnetic anisotropy as a layer in which domain wall motion occurs. In Non-Patent Document 4 below, observation of current-induced domain wall motion in a perpendicular magnetic film is reported.

[Non-Patent Document 4] Tanigawa, H. et al., “Current-Driven Domain
Wall Motion in CoCrPt Wires with Perpendicular Magnetic Anisotropy ”, Applied
Physics Express, Vol. 1, No. 1, January 11, 2008, p011301

  In addition, when manufacturing an MRAM using a perpendicular magnetization film, it is necessary to introduce a domain wall into a layer where domain wall movement occurs. However, in Non-Patent Document 4, a domain wall is introduced by providing a step in a layer where domain wall movement occurs. doing.

  In the domain wall introduction, that is, initialization method used in Non-Patent Document 4, regions having different magnetic characteristics are formed by providing a step in the perpendicular magnetization film, and the difference in coercivity between these regions is utilized. Domain walls are introduced by applying an external magnetic field in multiple steps. However, such a method is not only complicated, but also requires a sufficient margin for the magnetic field into which the domain wall is introduced, and is not suitable for manufacturing a large-scale memory system. In addition, in the magnetic wire having perpendicular magnetic anisotropy, a large magnetic field is applied to the domain wall introduced near the step in the direction parallel to the film surface. There is a concern that the pinning force of the domain wall becomes excessive due to this magnetic field. This is not preferable from the viewpoint of reducing the write current.

  A first object of the present invention is to provide a magnetic random access memory capable of introducing a domain wall by a simple and easy method.

  A second object of the present invention is to provide a magnetic random access memory capable of writing at a low current density by appropriately adjusting the pinning force of the domain wall.

  A magnetic random access memory according to one aspect of the present invention will be described. A magnetic random access memory according to one aspect of the present invention has a plurality of magnetic memory cells arranged in an array, and each magnetic memory cell has a magnetoresistive effect element.

  The magnetoresistive element according to one aspect of the present invention includes at least a first ferromagnetic layer and a second ferromagnetic layer group. The first ferromagnetic layer includes at least a first magnetization fixed region, a second magnetization fixed region, and a magnetization free region, and the first magnetization fixed region and the second magnetization fixed region are provided connected to the magnetization free region. The second ferromagnetic layer group includes a second ferromagnetic layer and a coupling layer. The second ferromagnetic layer and the coupling layer are adjacent to each other. The second ferromagnetic layer group is magnetically coupled to the first magnetization fixed region.

  The first ferromagnetic layer and the second ferromagnetic layer group have at least a portion of a ferromagnetic material having perpendicular magnetic anisotropy. The first magnetization fixed region and the second magnetization fixed region have magnetizations fixed in antiparallel directions to each other at least in part. The magnetization free region has reversible magnetization at least at a part, and faces a direction parallel to either the first magnetization fixed region or the second magnetization fixed region. In such a magnetization arrangement, a domain wall is introduced into the first ferromagnetic layer group.

  As described above, the second ferromagnetic layer group includes the second ferromagnetic layer and is magnetically coupled to the first magnetization fixed region. Furthermore, in the second ferromagnetic layer group, at least a part of the second ferromagnetic layer group has a magnetization fixed in an antiparallel direction to the magnetization of the first magnetization fixed region. In order to realize such magnetization in the antiparallel direction (Ferri coupling), the coupling layer magnetically couples the first magnetization fixed region and the second ferromagnetic layer in the antiparallel direction.

  In addition to the above-described components, additional ferromagnetic layers, nonmagnetic layers, conductive layers, and the like are provided as appropriate. However, at least one ferromagnetic layer and at least one nonmagnetic layer are provided.

  An external magnetic field is used as a method for initializing the memory state of the magnetoresistive effect element according to one aspect of the present invention. When a sufficiently large external magnetic field is applied to the magnetoresistive element in the direction perpendicular to the film surface, the magnetization free region, the second magnetization fixed region, and the second ferromagnetic layer face the direction of the external magnetic field, and the second ferromagnetic layer And the first magnetization fixed region that is ferrimagnetically coupled to face the opposite direction to the external magnetic field. As a result, a domain wall is introduced at the boundary between the first magnetization fixed region and the magnetization free region.

  As a method for writing information to the magnetoresistive effect element according to one aspect of the present invention, a current induced domain wall motion phenomenon is used.

  The magnetoresistive effect is used as a method for reading information from the magnetoresistive effect element according to one aspect of the present invention.

  Since the second magnetization fixed region and the second ferromagnetic layer are coupled ferrimagnetically, the memory state can be initialized by applying an external magnetic field once. Further, depending on the magnetic characteristics of the second magnetization fixed region and the second ferromagnetic layer, a two-step external magnetic field application step is required. In this case, a sufficiently large initialization margin can be obtained. That is, a domain wall can be introduced by a simple initialization process, and a large initialization magnetic field margin can be easily secured.

  As a second effect of the present invention, the write current can be reduced in the perpendicular magnetization domain wall motion type MRAM. This is because the influence of the magnetic field on the pin site of the domain wall can be adjusted by appropriately designing the leakage magnetic field in the step region to the configuration of the second ferromagnetic layer group (20).

The foregoing and other objects, advantages, and features of the present invention will become more apparent from the following description, taken in conjunction with the accompanying drawings, for several embodiments. The accompanying drawings include the following.
FIG. 1A is a perspective view showing the structure of the main part of a magnetoresistive effect element according to one embodiment of the present invention. FIG. 1B is a plan view showing the structure of the main part of the magnetoresistive effect element according to one embodiment of the present invention. FIG. 1C is a cross-sectional view showing the structure of the main part of the magnetoresistive effect element according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of the magnetization structure of the magnetoresistive effect element according to one embodiment of the present invention. FIG. 3A is a schematic diagram for explaining the principle of the initialization method used in the embodiment of the present invention. FIG. 3B is a schematic diagram for explaining the principle of the initialization method used in the embodiment of the present invention. FIG. 4A is a magnetization curve of a laminated film obtained by laminated ferrimagnetic coupling. FIG. 4B is a magnetization curve of a laminated film formed by laminated ferrimagnetic coupling. FIG. 4C is a magnetization curve of a laminated film formed by laminated ferrimagnetic coupling. FIG. 5 is a cross-sectional view for explaining a method of initializing the memory state of the magnetoresistive effect element according to one embodiment of the present invention. FIG. 6A is a cross-sectional view for explaining another method of initializing the memory state of the magnetoresistive effect element according to one embodiment of the present invention. FIG. 6B is a cross-sectional view for explaining another method of initializing the memory state of the magnetoresistive effect element according to the exemplary embodiment of the present invention. FIG. 7A is a cross-sectional view for explaining a method of writing information to the magnetoresistive element according to one embodiment of the present invention. FIG. 7B is a cross-sectional view for explaining a method of writing information to the magnetoresistive element according to one embodiment of the present invention. FIG. 8A is a cross-sectional view for explaining a method of reading information from the magnetoresistive effect element according to one embodiment of the present invention. FIG. 8B is a cross-sectional view for explaining a method of reading information from the magnetoresistive effect element according to one embodiment of the present invention. FIG. 9 is an example of a circuit diagram for one cell of the magnetic memory cell according to one embodiment of the present invention. FIG. 10A is a perspective view showing the structure of the main part of the first modification of the magnetoresistance effect element according to the present invention. FIG. 10B is a cross-sectional view showing the structure of the main part of the first modification of the magnetoresistance effect element according to the present invention. FIG. 10C is a cross-sectional view showing the structure of the main part of the first modification of the magnetoresistance effect element according to the present invention. FIG. 11A is a cross-sectional view showing the structure of the main part of a second modification of the magnetoresistive effect element according to the present invention. FIG. 11B is a schematic diagram for explaining the operation of the second modification of the magnetoresistance effect element according to the present invention. FIG. 11C is a schematic diagram for explaining the operation of the second modification of the magnetoresistance effect element according to the present invention. FIG. 12 is a cross-sectional view showing the structure of the main part of another second modification of the magnetoresistive effect element according to the present invention. FIG. 13 is a sectional view showing the structure of the main part of still another second modified example of the magnetoresistive effect element according to the present invention. FIG. 14A is a perspective view showing the structure of the main part of the third modification of the magnetoresistance effect element according to the present invention. FIG. 14B is a plan view showing the structure of the main part of the third modification of the magnetoresistance effect element according to the present invention. FIG. 15 is a cross-sectional view showing the structure of the main part of the third modification of the magnetoresistive effect element according to the present invention. FIG. 16 is a cross-sectional view showing the structure of the main part of another third modification of the magnetoresistance effect element according to the present invention. FIG. 17 is a cross-sectional view showing the structure of the main part of still another third modification of the magnetoresistance effect element according to the present invention. FIG. 18A is a perspective view showing the structure of the main part of a fourth modification of the magnetoresistance effect element according to the present invention. FIG. 18B is a plan view showing the structure of the main part of the fourth modification example of the magnetoresistance effect element according to the present invention. FIG. 18C is a cross-sectional view showing the structure of the main part of a fourth modification of the magnetoresistance effect element according to the present invention. FIG. 19A is a cross-sectional view for explaining a method of reading information in the fourth modified example. FIG. 19B is a cross-sectional view for explaining the information reading method in the fourth modified example. FIG. 20A is a plan view showing the structure of the main part of the fifth modification example of the magnetoresistance effect element according to the present invention. FIG. 20B is a plan view showing the structure of the main part of the fifth modification example of the magnetoresistance effect element according to the present invention. FIG. 21A is a plan view showing the structure of the main part of another fifth modification of the magnetoresistance effect element according to the present invention. FIG. 21B is a plan view showing the structure of the main part of another fifth modification of the magnetoresistance effect element according to the present invention. FIG. 22A is a plan view showing a structure of a main part of still another fifth modification example of the magnetoresistance effect element according to the present invention. FIG. 22B is a plan view showing the structure of the main part of still another fifth modification example of the magnetoresistance effect element according to the present invention. FIG. 23A is a plan view for explaining the information writing method in the fifth modification shown in FIGS. 22A and 22B. FIG. 23B is a plan view for explaining the information writing method in the fifth modification shown in FIGS. 22A and 22B.

  A magnetic random access memory according to an embodiment of the present invention will be described with reference to the accompanying drawings. The magnetic random access memory according to the present embodiment has a plurality of magnetic memory cells arranged in an array, and each magnetic memory cell has a magnetoresistive effect element.

(Construction)
1A, 1B, and 1C schematically show an example of an embodiment of a main part of a magnetoresistive effect element according to the present invention. 1A is a perspective view, and FIG. 1B and FIG. 1C are an xy plan view and an xz sectional view in the xyz coordinate system shown in FIG. 1A.

  The magnetoresistive effect element according to the present embodiment includes at least a first ferromagnetic layer 10 and a second ferromagnetic layer group 20. The first ferromagnetic layer 10 includes at least a first magnetization fixed region 11a, a second magnetization fixed region 11b, and a magnetization free region 12. The first magnetization fixed region 11 a and the second magnetization fixed region 11 b are provided in connection with the magnetization free region 12. 1A, 1B, and 1C, a first magnetization fixed region 11a is provided connected to one end of the magnetization free region 12, and a second magnetization fixed region 11b is provided connected to the other end. Yes. The second ferromagnetic layer group 20 includes a second ferromagnetic layer 21 and a coupling layer 22. The second ferromagnetic layer 21 and the coupling layer 22 are adjacent to each other. The second ferromagnetic layer group 20 is magnetically coupled to the first magnetization fixed region 11a. In FIG. 1A, FIG. 1B, and FIG. 1C, the coupling layer 22 is provided adjacent to the first magnetization fixed region 11a, and the second ferromagnetic layer 21 is adjacent to the coupling layer 22 and opposite to the first magnetization fixed region 11a. Is provided.

  The first ferromagnetic layer 10 and the second ferromagnetic layer group 20 have at least a portion of a ferromagnetic material having perpendicular magnetic anisotropy. Further, at least a part of the first magnetization fixed region 11a has a magnetization fixed in an antiparallel direction with respect to at least a part of the second magnetization fixed region 11b. The magnetization free region 12 has reversible magnetization at least partially. This reversible magnetization is oriented in a direction parallel to either the first magnetization fixed region 11a or the second magnetization fixed region 11b. In such a magnetization arrangement, a domain wall is introduced into the first ferromagnetic layer group.

  As described above, the second ferromagnetic layer group 20 includes the second ferromagnetic layer 21 and is magnetically coupled to the first magnetization fixed region 11a. Further, the second ferromagnetic layer group 20 has a magnetization fixed in an antiparallel direction to the magnetization of the first magnetization fixed region 11a at least in part. In order to realize such antiparallel magnetization, the coupling layer 22 magnetically couples the first magnetization fixed region 11a and the second ferromagnetic layer 21 in the antiparallel direction.

  FIG. 2 schematically shows an example of the magnetization state of the main part of the magnetoresistive effect element according to the present embodiment. In FIG. 2, the first magnetization fixed region 11a has magnetization fixed in the z-axis positive direction, and the second magnetization fixed region 11b has magnetization fixed in the z-axis negative direction. The magnetization free region 12 has a magnetization that can take either the z-axis positive or negative direction. Further, in the second ferromagnetic layer group 20 provided adjacent to the first magnetization fixed region 11a, the second ferromagnetic layer 21 has a negative z-axis that is antiparallel to the magnetization of the first magnetization fixed region 11a. It has a magnetization fixed in the direction.

  An example of a ferromagnetic material used for the first ferromagnetic layer 10 and the second ferromagnetic layer group 20 is a Co—Pt alloy. An example of the material used for the bonding layer 22 is Ru.

  Although not shown in the drawing, in addition to the above-described components, a further ferromagnetic layer, nonmagnetic layer, conductive layer, and the like are provided, but these are optional. However, at least one ferromagnetic layer and at least one nonmagnetic layer are provided. These specific forms will be described later. Each layer is desirably provided with a base layer, a cap layer, etc. adjacent to each other as necessary, but this is omitted.

(principle)
In the present embodiment, in an MRAM using domain wall motion, a laminated antiferromagnetic coupling (SyAF Coupling) is applied as an initialization method. The laminated ferrimagnetic coupling will be described below with reference to FIGS. 3A and 3B.

  Consider a laminated film in which a ferromagnetic layer A, a coupling layer, and a ferromagnetic layer B as shown in FIG. 3A are laminated in this order. When a specific material is used as the coupling layer, the coupling strength between the ferromagnetic layer A and the ferromagnetic layer B attenuates while oscillating with respect to the change in the thickness of the coupling layer as shown in FIG. 3B. It has been known. This is often referred to as RKKY interaction. Examples of the material of the bonding layer that exhibits the RKKY interaction include Ru, Cr, Cu, Ir, Os, and Re.

  Referring to FIG. 3B, when the thickness of the coupling layer is 0, ferromagnetic, ie, a parallel coupling force acts between the ferromagnetic layer A and the ferromagnetic layer B. Increasing the thickness of the coupling layer is ferrimagnetic, that is, an anti-parallel coupling force acts between the ferromagnetic layer A and the ferromagnetic layer B, and further increasing the thickness, ferromagnetic, Repeats ferrimagnetic coupling. For this reason, in the case of the present embodiment, by setting the material and film thickness of the coupling layer 22 appropriately, antiparallel magnetic coupling can be obtained between the upper and lower layers. The state can be easily initialized.

  Specific measurement results of the magnetization curve in the laminated film as shown in FIGS. 3A and 3B are shown in FIGS. 4A, 4B, and 4C. In the experiment, a material having perpendicular magnetic anisotropy was used for both the ferromagnetic layer A and the ferromagnetic layer B, and an external magnetic field was applied in a direction perpendicular to the substrate surface. FIG. 4A is a magnetization curve in a certain film configuration. 4B and 4C are magnetization curves in different film configurations, FIG. 4B shows the major loop, and FIG. 4C shows the minor loop.

  In FIG. 4A, in the state (1), the ferromagnetic layer A and the ferromagnetic layer B are magnetized in parallel to each other, and this is magnetized in the antiparallel direction in the state of 0 magnetic field in (2). Recognize. In FIG. 4B, magnetization is performed in the parallel direction in the state of the positive magnetic field (1), magnetized in the anti-parallel state in the state of the negative magnetic field in (2), and when the negative magnetic field is further increased, the parallel magnetization state is obtained again. It can be seen that the transition occurs. Further, as shown in FIG. 4C, it can be seen that in the magnetization curve of FIG. 4B, when the negative magnetic field is reduced from the state of (2) and set to 0, the anti-parallel state is obtained even at 0 magnetic field.

  Although a method using the RKKY interaction has been described here as a method for obtaining antiparallel coupling, any mechanism may be used as long as antiparallel coupling is actually obtained.

(Initialization method)
Next, a method for initializing the memory state of the magnetoresistive effect element according to the present embodiment will be described. FIG. 5 shows an example of a memory state initialization method in the structure shown in FIGS. 1A to 2.

  In the initialization method shown in FIG. 5, the memory state is initialized by applying an external magnetic field once. FIG. 5 shows an example in which a magnetic field is applied in the −z direction as the external magnetic field. Consider a case where a sufficiently large external magnetic field is applied to the magnetoresistive element as shown in FIGS. 1A to 2 in the −z direction. At this time, the magnetizations of the second magnetization fixed region 11b and the magnetization free region 12 are oriented in the same direction as the external magnetic field, and are thus magnetized in the −z direction. Next, the first magnetization fixed region 11a and the second ferromagnetic layer group 20 will be considered. The first magnetization fixed region 11 a is ferrimagnetically coupled to the second ferromagnetic layer 21 through the coupling layer 22. Here, when the magnetization of the second ferromagnetic layer 21 is larger than the magnetization of the first magnetization fixed region 11 (more strictly, when the product of the saturation magnetization and the film thickness is larger in the second ferromagnetic layer 21). The magnetization of the second ferromagnetic layer 21 is preferentially directed in the direction of the external magnetic field, that is, in the −z direction, whereby the magnetization of the first magnetization fixed region 11a is directed in the opposite direction to the external magnetic field, that is, in the + z direction. In this way, the magnetized state as shown in FIG. 5 is realized. As can be seen from FIG. 5, a single domain wall is introduced into the first ferromagnetic layer 10, which means one memory state in the magnetoresistive element. The initialization method as shown in FIG. 5 can be applied when the magnetization curve of the laminated film formed of the first magnetization fixed region 11a and the second ferromagnetic layer group 20 has a shape as shown in FIG. 4A. .

  On the other hand, when the magnetization curve of the laminated film formed of the first magnetization fixed region 11a and the second ferromagnetic layer group 20 has a shape as shown in FIGS. 4B and 4C, as shown in FIGS. 6A and 6B. The memory state can be initialized by various initialization methods. First, when a sufficiently large external magnetic field is applied in the −z direction, all magnetizations are directed in the external magnetic field direction, that is, the −z direction. This state corresponds to the state (1) in the magnetization curve of FIG. 4C. Next, even when this external magnetic field is set to 0, all the magnetizations remain in the −z direction as shown in FIG. 6A. This corresponds to the state (1) ′ in the magnetization curve of FIG. 4C. Next, as shown in FIG. 6B, a relatively small external magnetic field is applied in the + z direction. At this time, an antiparallel state corresponding to (2) of the magnetization curve of FIG. 4C is realized, and only the magnetization of the first magnetization fixed region 11a is directed in the + z direction. Next, even if this external magnetic field is returned to 0, the antiparallel state corresponding to (3) of the magnetization curve in FIG. 4C is maintained, and the magnetization state as shown in FIG. 6B is realized. In FIG. 6B, a single domain wall is introduced into the first ferromagnetic layer 10, which means that the memory state is initialized.

  Note that the above-described conditions relating to the product of saturation magnetization and film thickness are not essential in the present invention. So far, the case where the product of the saturation magnetization and the film thickness of the second ferromagnetic layer 21 is larger than the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a has been described. A case where the product of the saturation magnetization and the film thickness of the second ferromagnetic layer 21 is smaller than the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a will be described. In this case, when a sufficiently large magnetic field is first applied in the downward direction, the magnetization of all regions is directed downward. Subsequently, when the external magnetic field is changed upward and the value thereof is increased, first, the magnetization of the second ferromagnetic layer 21 having a small product of the saturation magnetization and the film thickness is directed to the external magnetic field direction, that is, the upward direction. When the external magnetic field in the upward direction is further increased thereafter, the second magnetization fixed region 11b and the magnetization free region 12 have less antiparallel magnetic coupling with the second ferromagnetic layer 21 than the first magnetization fixed region 11a. Inversion occurs earlier, and the magnetizations of the second magnetization fixed region 11b and the magnetization free region 12 are directed upward. At this time, a domain wall is formed at the boundary between the first magnetization fixed region 11 a and the magnetization free region 12. In this way, the memory state can be initialized. As described above, in the present invention, it is possible to initialize the memory state by appropriately setting the external magnetic field application process regardless of the conditions regarding the product of the saturation magnetization and the film thickness. The same can be said for all of the modifications.

  In addition, the memory state may be initialized by applying an external magnetic field in several steps. The external magnetic field may have an in-plane direction component.

(Writing method)
Next, a method of writing information to the magnetoresistive effect element according to the present embodiment will be described with reference to FIGS. 7A and 7B. As described above, in the first ferromagnetic layer 10 forming the magnetoresistive effect element according to the present embodiment, a domain wall is formed according to the magnetization direction of the magnetization free region 12. In the magnetoresistive effect element according to the present embodiment, information is written by driving the domain wall with current. 7A and 7B show an example of the method. FIG. 7A shows a method of writing “1” from the “0” state, and FIG. 7B shows a method of writing “0” from the “1” state.

  As shown in FIG. 7A, the magnetization of the first magnetization fixed region 11a is fixed upward, the magnetization of the second magnetization fixed region 11b is fixed downward, and the magnetization of the magnetization free region 12 is directed downward. Is defined as a “0” state. As shown in FIG. 7B, a state where the magnetization of the magnetization free region 12 is directed upward is defined as a “1” state. However, the definition of “0” state and “1” state is not limited to this.

  In the “0” state of FIG. 7A, a domain wall (DW) is formed at the boundary between the first magnetization fixed region 11 a and the magnetization free region 12. As indicated by the dotted line in the figure, a write current is introduced in the direction from the second magnetization fixed region 11b to the first magnetization fixed region 11a via the magnetization free region 12. At this time, the conduction electrons flow from the first magnetization fixed region 11a to the second magnetization fixed region 11b via the magnetization free region 12. The conduction electrons cause current-induced domain wall movement, and the domain wall (DW) moves from the boundary between the first magnetization fixed region 11a and the magnetization free region 12 to the boundary between the second magnetization fixed region 11b and the magnetization free region 12, and FIG. As shown in FIG. In this way, “1” is written. A mechanism in which the domain wall (DW) stops at the boundary between the second magnetization fixed region 11b and the magnetization free region 12 will be described later.

  In the “1” state of FIG. 7B, a domain wall (DW) is formed at the boundary between the second magnetization fixed region 11 b and the magnetization free region 12. Here, as indicated by a dotted line in the figure, a write current is introduced in the direction from the first magnetization fixed region 11a to the second magnetization fixed region 11b via the magnetization free region 12. At this time, conduction electrons flow in a direction from the second magnetization fixed region 11b to the first magnetization fixed region 11a via the magnetization free region 12. This conduction electron causes current-induced domain wall movement, and the domain wall (DW) moves from the boundary between the second magnetization fixed region 11b and the magnetization free region 12 to the boundary between the first magnetization fixed region 11a and the magnetization free region 12, and FIG. As shown in FIG. In this way, “0” is written.

  In order to use such a writing method, the first magnetization fixed region 11a and the second magnetization fixed region 11b are preferably connected to different external wirings.

  Although not shown, “0” writing from the “0” state and “1” writing from the “1” state, that is, overwriting is also possible.

  In writing, the domain wall cannot pass through the boundary between the magnetization fixed region 11 and the magnetization free region 12 and enter the magnetization fixed region 11. This is because the current density decreases in the magnetization fixed region 11. Specifically, it will be described as follows. In the magnetization fixed region 11, an electrode for introducing a write current is desirably provided adjacent to the upper surface or the lower surface. 7A and 7B show a structure in which the electrode layer 50 is provided adjacent to the lower surfaces of the first magnetization fixed region 11a and the second magnetization fixed region 11b as an example. At this time, the write current flows to the electrode layer 50, and the cross-sectional area perpendicular to the current direction increases outside the boundary between the magnetization fixed region 11 and the magnetization free region 12. Therefore, the current density is reduced and becomes smaller than the threshold current density necessary for the current-induced domain wall movement, so that the domain wall movement does not occur and stops there.

  The reduction in current density due to such an increase in cross-sectional area can also be controlled by modulation of the xy plane shape. For example, the current density outside the boundary between the magnetization fixed region 11 and the magnetization free region 12 can be reduced by setting the width of the magnetization fixed region 11 wider than the width of the magnetization free region 12. A suitable shape for this will be described in a later-described modification.

  In addition, the domain wall stopped at the boundary between the magnetization fixed region 11 and the magnetization free region 12 can stably remain in place. This is because in a material having perpendicular magnetic anisotropy, there are innumerable pinning sites and they have sufficiently large thermal stability.

(Reading method)
Next, a method of reading information from the magnetoresistive effect element according to the present exemplary embodiment will be described with reference to FIGS. 8A and 8B. As described above, in the magnetoresistive effect element according to the present exemplary embodiment, information is stored according to the magnetization direction of the magnetization free region 12 of the first ferromagnetic layer 10. In the magnetoresistive effect element according to the present embodiment, information is read by detecting the magnetization of the magnetization free region 12 using the magnetoresistive effect. 8A and 8B show an example of the method. FIG. 8A shows a reading method in the “0” state, and FIG. 8B shows a reading method in the “1” state.

  In the present embodiment, at least one additional ferromagnetic layer and at least one nonmagnetic layer are provided to read information. 8A and 8B show an example of the structure of the magnetoresistive element according to this embodiment. As shown in FIGS. 8A and 8B, in the magnetoresistive effect element according to the present exemplary embodiment, the first nonmagnetic layer 30 is provided adjacent to the magnetization free region 12 of the first ferromagnetic layer 10, and A third ferromagnetic layer 40 is provided adjacent to the nonmagnetic layer 30 on the side opposite to the magnetization free region 12. The first ferromagnetic layer 10, the first nonmagnetic layer 30, and the second ferromagnetic layer 20 form a magnetic tunnel junction (MTJ).

  The first nonmagnetic layer 30 is made of a nonmagnetic material and is preferably made of an insulating material, but may be made of a semiconductor or a metal material. A specific material of the first nonmagnetic layer 30 is exemplified by Al—O. The third ferromagnetic layer 40 is made of a ferromagnetic material having perpendicular magnetic anisotropy. Furthermore, the magnetization of the third ferromagnetic layer 40 is substantially fixed in one direction. Although the third ferromagnetic layer 40 is depicted as a single-layer ferromagnetic layer in FIGS. 8A and 8B, it may actually be formed of a laminated film composed of a plurality of ferromagnetic layers. May include a nonmagnetic layer. Adjacent ferromagnetic layers may be magnetically coupled in the antiparallel direction by a nonmagnetic layer disposed in the middle. Furthermore, the magnetization can be fixed more firmly by making the antiferromagnetic layer adjacent. Examples of the laminated configuration of the third ferromagnetic layer 40 include Co—Pt / Ru / Co—Pt / PtMn.

  Now, as shown in FIGS. 8A and 8B, the third ferromagnetic layer 40 (or the vicinity of the interface of the third ferromagnetic layer 40 with the first nonmagnetic layer 30) is fixed downward. To do. Here, as shown in FIG. 8A, consider the “0” state in which the magnetization free region 12 is magnetized downward. In this state, when current is introduced in a direction penetrating the first ferromagnetic layer 10, the first nonmagnetic layer 30, and the third ferromagnetic layer 40, the magnetizations of the magnetization free region 12 and the third ferromagnetic layer 40 are parallel. Therefore, the MTJ resistance in this case is low. On the other hand, as shown in FIG. 8B, consider the “1” state in which the magnetization free region 12 is magnetized upward. In this state, when current is introduced in a direction penetrating the first ferromagnetic layer 10, the first nonmagnetic layer 30, and the third ferromagnetic layer 40, the magnetizations of the magnetization free region 12 and the third ferromagnetic layer 40 are antiparallel. Therefore, the MTJ resistance in this case is high. Thus, by detecting the difference in resistance when a current is passed through the MTJ, the magnetization direction of the magnetization free region 12 can be detected, and information can be read from the magnetoresistive effect element. Can do.

  The positions of the first nonmagnetic layer 30 and the third ferromagnetic layer 40 are arbitrary. In FIGS. 8A and 8B, the first nonmagnetic layer 30 and the third ferromagnetic layer 40 are disposed below the first ferromagnetic layer 10. It does not matter. Moreover, the same side as a 2nd ferromagnetic layer group may be sufficient, and the other side may be sufficient.

(effect)
As a first effect of the present embodiment, a perpendicular domain wall motion type MRAM capable of easily initializing a memory state is provided. Generally, as a method for introducing a domain wall in a perpendicular magnetization film, it is conceivable to provide a step as shown in Non-Patent Document 4. That is, regions having different magnetic characteristics are formed by providing a step in the perpendicular magnetization film, and a domain wall is introduced by applying an external magnetic field in a plurality of steps using the difference in coercivity between these regions. However, such a method is not only complicated, but also requires a sufficient margin for the magnetic field into which the domain wall is introduced, and is not suitable for manufacturing a large-scale memory. However, when this embodiment is used, the domain wall can be introduced by a simple initialization process, and a large initialization magnetic field margin can be easily secured.

  As a second effect of the present embodiment, the write current can be reduced in the perpendicular magnetic domain wall motion type MRAM. When the method of pinning the domain wall by a step as used in Non-Patent Document 4 is used, there is a concern that a large leakage magnetic field is applied from the magnetization fixed region in the step region, which becomes an excessive domain wall pinning force. Is done. However, according to the present embodiment, since the influence of the magnetic field on the domain wall pin site is reduced, adjustment can be made so that an excessive domain wall pinning force does not work. This reduces the current density required to depin the domain wall from the pin site, resulting in a reduction in the current value required for writing. Note that the second effect is more effectively brought about by appropriately designing the laminated structure of the second ferromagnetic layer group 20. Details will be described later in the second modification.

(Circuit configuration)
Next, a circuit configuration for introducing a write current and a read current in the magnetic memory cell constituted by the magnetoresistive effect element according to the present embodiment will be described.

  FIG. 9 shows a configuration example of a circuit for one bit of the magnetic memory cell according to the present embodiment. In FIG. 9, only the first ferromagnetic layer 10, the first nonmagnetic layer 30, and the third ferromagnetic layer 40 of the magnetoresistive effect element are shown.

  As shown in FIG. 9, the terminal connected to the third ferromagnetic layer 40 is connected to the ground line 101 for reading. On the other hand, two terminals connected to the first magnetization fixed region 11a and the second magnetization fixed region 11b are connected to one source / drain of two different transistors 100a and 100b, respectively. The other source / drain of the transistors 100a and 100b is connected to the bit lines 102a and 102b for writing, and the gate electrode is connected to the common word line 103. Further, the magnetic memory cells shown in FIG. 9 are arranged in an array and connected to a peripheral circuit to form a magnetic random access memory (MRAM).

  Next, writing and reading methods in the circuit shown in FIG. 9 will be described. First, when writing, the word line 103 is set to “high” and the transistors 100a and 100b are set to “ON”. One of the bit lines 102a and 102b is set to “high”, and the other is set to “ground”. Since the direction of the current flowing through the first ferromagnetic layer 10 changes depending on which bit line 102 is set to “high” and which is set to “ground”, information can be written to the magnetoresistive element. It becomes.

  At the time of reading, the word line 103 is set to “high”, and the transistors 100a and 100b are set to “ON”. Further, the bit line 102a is set to “open”, and the bit line 102b is set to “high”. At this time, a current passing through the magnetoresistive effect element from the bit line 102b flows to the ground line 101 via the first ferromagnetic group layer 10, the first nonmagnetic layer 30, and the third ferromagnetic layer 40. High-speed reading using the effect is possible.

  However, the setting of the circuit shown in FIG. 9 and the circuit described here is merely an example of a method for carrying out the present invention, and other circuit configurations are possible.

(material)
Next, the material of each layer is illustrated. Note that all the materials shown here are examples, and any material may be used in practice as long as the above-described magnetization state can be realized.

  First, as described above, the first ferromagnetic layer 10 and the second ferromagnetic layer group 30 include a ferromagnetic layer having perpendicular magnetic anisotropy. These ferromagnetic layers are composed of a ferromagnetic material including at least one material selected from Fe, Co, and Ni. Moreover, perpendicular magnetic anisotropy can be stabilized by including Pt and Pd. In addition to this, B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W, By adding Re, Os, Ir, Au, Sm or the like, it is possible to adjust so that desired magnetic properties are expressed. Specifically, Co, Co—Pt, Co—Pd, Co—Cr, Co—Pt—Cr, Co—Cr—Ta, Co—Cr—B, Co—Cr—Pt—B, Co—Cr—Ta— B, Co-V, Co-Mo, Co-W, Co-Ti, Co-Ru, Co-Rh, Fe-Pt, Fe-Pd, Fe-Co-Pt, Fe-Co-Pd, Sm-Co, Examples include Gd—Fe—Co, Tb—Fe—Co, and Gd—Tb—Fe—Co. In addition, the magnetic anisotropy in the perpendicular direction can also be exhibited by laminating a layer containing any one material selected from Fe, Co, and Ni with different layers. Specifically, a laminated film of Co / Pd, Co / Pt, Co / Ni, Fe / Au, and the like are exemplified.

  The first nonmagnetic layer 30 is preferably made of an insulating material. Specifically, Mg-O, Al-O, Al-N, Ni-O, Hf-O, etc. are illustrated. However, the present invention can also be implemented using a semiconductor or a metal material. Specifically, Al, Cr, Cu and the like are exemplified.

  As described above, the magnetization fixed can be further strengthened by making the third ferromagnetic layer 40 adjacent to the antiferromagnetic layer. Specific examples of the antiferromagnetic material include Pt—Mn, Ir—Mn, and Fe—Mn.

  The bonding layer 22 is preferably made of a material that expresses the RKKY interaction. Specifically, Ru, Cr, Cu, Ir, Os, Re, etc. are illustrated.

(First modification)
10A and 10B schematically show the structure of a first modification of the magnetoresistance effect element according to the present invention. The first modification relates to the position of the second ferromagnetic layer group 20. 10A is a perspective view, and FIG. 10B is an xz sectional view in the xyz coordinate system shown in FIG. 10A.

  In the magnetoresistive effect element according to the above-described embodiment of the present invention, the second ferromagnetic layer group 20 is provided adjacent to the first magnetization fixed region 11a, but this position is optional. That is, FIGS. 1A to 1C show an example in which the second ferromagnetic layer group 20 is disposed above the first ferromagnetic layer 10, as shown in FIGS. 10A and 10B. It may be on the lower side.

  FIG. 10C shows a cross-sectional view of another embodiment relating to the first modification. A Co-based alloy is known as a material having perpendicular magnetic anisotropy, and Ru is often used as a base layer of the Co-based alloy. FIG. 10C shows an example in which the coupling layer 22 also serves as the underlayer of the first ferromagnetic layer 10. By using Ru or the like as the coupling layer 22, the second ferromagnetic layer 21 and the first ferromagnetic layer 10 are coupled by laminated ferrimagnetic coupling, and at the same time, the first ferromagnetic layer 10 is used as an underlayer of the first ferromagnetic layer 10. The crystal orientation of the layer 10 can be adjusted.

(Second modification)
11A to 13 schematically show the structure of a second modification of the magnetoresistance effect element according to the present invention. The second modification relates to the configuration of the second ferromagnetic layer group 20.

  In the magnetoresistive effect element according to the present invention, the configuration of the second ferromagnetic layer group 20 is arbitrary. FIG. 11A is a cross-sectional view showing an example. As shown in FIG. 11A, the second ferromagnetic layer group 20 may be a stacked film including a fourth ferromagnetic layer 23 in addition to the first ferromagnetic layer 10 and the coupling layer 22. In FIG. 11A, the fourth ferromagnetic layer 23 is provided adjacent to the first magnetization fixed region 11a. Adjacent to the fourth ferromagnetic layer 23, a coupling layer 22 and a second ferromagnetic layer 21 are provided in this order on the opposite side to the first magnetization fixed region 11a. The first magnetization fixed region 11 a and the fourth ferromagnetic layer 23 are ferromagnetically coupled, and the second ferromagnetic layer 21 and the fourth ferromagnetic layer 23 are ferrimagnetically coupled via the coupling layer 22. Yes. For example, the RKKY interaction described above is used for the ferrimagnetic magnetic coupling.

  In the structure shown in FIG. 11A, the product of the saturation magnetization and film thickness of the second ferromagnetic layer 21 is the product of the saturation magnetization and film thickness of the first magnetization fixed region 11a and the saturation magnetization of the fourth ferromagnetic layer 23. It is preferably larger than the sum of the product of film thicknesses. This is because the memory state can be initialized by such a method by applying an external magnetic field similar to the method described with reference to FIG. 5, FIG. 6A or FIG. 6B.

  Further, by using the configuration as shown in FIG. 11A, the write current density can be more effectively reduced. In FIG. 11B and FIG. 11C, the state of the magnetic field formed in the vicinity of the first ferromagnetic layer 10 by the magnetization of the second ferromagnetic layer 21 and the fourth ferromagnetic layer 23 is schematically represented by arrows. 11B and 11C are applied to the first ferromagnetic layer 10. As can be seen from FIGS. 11B and 11C, in the vicinity of the boundary between the first magnetization fixed region 11a and the magnetization free region 12, The magnetic field in the x direction cancels and becomes smaller. There is a concern that the magnetic field in the x direction may cause an excessive pinning force. However, by implementing this modification, the excessive pinning force is suppressed, and writing with a smaller current density is possible. Moreover, the magnitude of this pinning force can be adjusted by appropriately designing the magnetic properties and film thicknesses of the second ferromagnetic layer 21 and the fourth ferromagnetic layer 23.

  FIG. 12 is a cross-sectional view showing an example of another embodiment of the second modification of the magnetoresistance effect element according to the present invention. As shown in FIG. 12, the second ferromagnetic layer group 20 is a laminated film including a second coupling layer 24 and a fourth ferromagnetic layer 23 in addition to the first ferromagnetic layer 10 and the first coupling layer 22. Also good. In FIG. 12, the first coupling layer 22 is provided adjacent to the first magnetization fixed region 11a. Adjacent to the first coupling layer 22, a second ferromagnetic layer 21, a second coupling layer 24, and a fourth ferromagnetic layer 23 are stacked in this order. The first magnetization fixed region 11a and the second ferromagnetic layer 21 are ferrimagnetically coupled via the first coupling layer 22, and the second ferromagnetic layer 21 and the fourth ferromagnetic layer 23 are the second coupling layer. It is ferrimagnetically coupled through 24.

  Also in the structure shown in FIG. 12, the memory state can be initialized by the external magnetic field application process as described above with reference to FIGS.

  Also in the structure shown in FIG. 12, the same effects as those described with reference to FIGS. 11B and 11C are obtained, and a reduction in write current is expected.

  Next, FIG. 13 is a sectional view showing still another embodiment of the second modification of the magnetoresistive effect element according to the present invention. As shown in FIG. 13, the second ferromagnetic layer group 20 may be a laminated film including an antiferromagnetic layer 25 in addition to the first ferromagnetic layer 10 and the coupling layer 22. In FIG. 13, the coupling layer 22 is provided adjacent to the first magnetization fixed region 11a. A second ferromagnetic layer 21 and an antiferromagnetic layer 25 are stacked adjacent to the coupling layer 22 in this order. The first magnetization fixed region 11 a and the second ferromagnetic layer 21 are ferrimagnetically coupled via the coupling layer 22.

  It is known that when an antiferromagnetic layer is placed adjacent to a ferromagnetic material and heat treatment is performed in a magnetic field, the magnetization of the ferromagnetic material is fixed in the direction of the magnetic field during the heat treatment. This antiferromagnetic layer-ferromagnetic coupling is often called exchange bias coupling. In the embodiment shown in FIG. 13, this exchange bias coupling is applied to the second ferromagnetic layer group 20. In the initialization process by the external magnetic field shown in FIG. 5 or FIG. 6A, when the external magnetic field is applied for a certain period of time while being kept at a high temperature, the antiferromagnetic layer 25 and the second ferromagnetic layer 21 are exchanged. Bias coupling works. As a result, the fixed magnetization of the second ferromagnetic layer 21 becomes stronger. As a result, the magnetization of the first magnetization fixed region 11a can be more firmly fixed. In addition, the margin of the initialization magnetic field can be further increased.

  For the antiferromagnetic layer 25, Pt—Mn, Ir—Mn, Fe—Mn, or the like can be used.

(Third Modification)
14A to 17 schematically show the structure of a third modification of the magnetoresistance effect element according to the present invention. In the third modification, a plurality of second ferromagnetic layer groups 20 are provided. FIG. 14A is a perspective view, and FIG. 14B is an xy plan view in the xyz coordinate system shown in FIG. 14A. FIGS. 15 to 17 show xz sectional views in the xyz coordinate system shown in FIG. 14A, which show different embodiments in the third modification.

  In the magnetoresistive effect element according to this modification, a plurality of second ferromagnetic layer groups 20 may be provided. In FIG. 14A to FIG. 17, as an example of the third modification, the 2-1 ferromagnetic layer group 20a is provided adjacent to the first magnetization fixed region 11a, and the other is adjacent to the second magnetization fixed region 11b. An example is shown in which a 2-2 ferromagnetic layer group 20b, which is a ferromagnetic layer group, is provided.

  In FIG. 15, the 2-1 ferromagnetic layer group 20a is formed of the 2-1 ferromagnetic layer 21a and the 1-1 coupling layer 22a, and the 2-2 ferromagnetic layer group 20b is the 2-2 ferromagnetic layer. An example formed from 21b and the 1-2 coupling layer 22b is shown. The first magnetization fixed region 11a and the 2-1 ferromagnetic layer 21a are ferrimagnetically coupled via the 1-1 coupling layer 22a, and the second magnetization fixed region 11b and the 2-2 ferromagnetic layer 21b are coupled. Are ferrimagnetically coupled through the 1-2 coupling layer 22b.

  The saturation magnetization or film thickness of the 2-1 ferromagnetic layer 21a and the 2-2 ferromagnetic layer 21b is preferably different. More preferably, the product of the saturation magnetization and the film thickness of the 2-1 ferromagnetic layer 21a is larger than the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a, while the saturation of the 2-2 ferromagnetic layer 21b. The product of magnetization and film thickness is preferably smaller than the product of saturation magnetization and film thickness of the second magnetization fixed region 11b. Consider a case where an external magnetic field in the −z direction as shown in FIG. 5 is applied under such conditions. At this time, the product of the saturation magnetization and the film thickness of the 2-1 ferromagnetic layer 21a is larger than the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a. Therefore, the magnetization of the 2-1 ferromagnetic layer 21a faces the -z direction, which is the direction of the external magnetic field, and the magnetization of the first magnetization fixed region 11a ferricoupled to it faces the + z direction, which is the antiparallel direction. On the other hand, the product of the saturation magnetization and film thickness of the 2-2 ferromagnetic layer 21b is smaller than the product of the saturation magnetization and film thickness of the second magnetization fixed region 11b. Therefore, the magnetization of the second magnetization fixed region 11b faces the -z direction that is the direction of the external magnetic field, and the magnetization of the 2-2 ferromagnetic layer 21b that is ferricoupled to the second magnetization fixed region 11b faces the + z direction that is the antiparallel direction. In this way, the magnetizations of the first magnetization fixed region 11a and the second magnetization fixed region 11b can be directed in the antiparallel direction.

  In the structure as shown in FIG. 15, after the 2-1 ferromagnetic layer group 20a and the 2-2 ferromagnetic layer group 20b are simultaneously formed, only the 2-2 ferromagnetic layer group 20b is etched much. Can be easily manufactured.

  FIG. 16 shows an example of another embodiment of the third modification. In the form shown in FIG. 16, the 2-1 ferromagnetic layer group 20a is formed of a 2-1 ferromagnetic layer 21a, a 1-1 coupling layer 22a, and a 4-1 ferromagnetic layer 23a. -2 shows an example in which the ferromagnetic layer group 20b is formed of the 4-2 ferromagnetic layer 23b.

  In the structure shown in FIG. 16, the product of the saturation magnetization and the film thickness of the 2-1 ferromagnetic layer 21a is the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a and the 4-1 ferromagnetic layer 23a. It is preferably larger than the sum of the product of saturation magnetization and film thickness. This is because the memory state can be initialized by such a method by applying an external magnetic field similar to the method described with reference to FIG. 5, FIG. 6A or FIG. 6B. Details thereof will be omitted because they are obvious from the above description.

  In the structure shown in FIG. 16 as well, after the 2-1 ferromagnetic layer group 20a and the 2-2 ferromagnetic layer group 20b are simultaneously formed, only the 2-2 ferromagnetic layer group 20b is etched much. Can be easily manufactured.

  FIG. 17 shows still another example of the third modification. In the form shown in FIG. 17, the 2-1 ferromagnetic layer group 20a is formed of the 2-1 ferromagnetic layer 21a and the 1-1 coupling layer 22a, and the 2-2 ferromagnetic layer group 20b is the first layer. An example formed from the 2-2 ferromagnetic layer 21b is shown.

  In the structure shown in FIG. 17, it is preferable that the product of the saturation magnetization and the film thickness of the 2-1 ferromagnetic layer 21a is larger than the product of the saturation magnetization and the film thickness of the first magnetization fixed region 11a. This is because the memory state can be initialized by such a method by applying an external magnetic field similar to the method described with reference to FIG. 5, FIG. 6A or FIG. 6B. Details thereof will be omitted because they are obvious from the above description.

  In the structure shown in FIG. 17, after the film formation up to the 1-1st coupling layer 22a, only the magnetization free region 12 and the second magnetization fixed region 11b are removed by etching, and then the 2-1 ferromagnetic layer. 21a and the 2-2 ferromagnetic layer 21b can be formed simultaneously.

  By using the configuration shown in FIG. 17, the magnetizations of the first magnetization fixed region 11a and the second magnetization fixed region 11b can be more firmly fixed. In addition, the margin of the external magnetic field for initialization can be expanded.

(Fourth modification)
18A, 18B and 18C schematically show the structure of a fourth modification of the magnetoresistive element according to the invention. The fourth modification relates to the MTJ for reading the magnetoresistive effect element according to the present invention. 18A is a perspective view, and FIGS. 18B and 18C respectively show an xy plan view and an xz cross-sectional view in the xyz coordinate system shown in FIG. 18A.

  As described with reference to FIGS. 8A and 8B, in the embodiment of the present invention, information is read using the magnetoresistive effect. The MTJ at this time may not include the third ferromagnetic layer 40 as shown in FIGS. 8A and 8B. 18A, 18B, and 18C, in addition to the first ferromagnetic layer 10, the fifth ferromagnetic layer 210, the second nonmagnetic layer 220, and the sixth ferromagnetic layer 230 are used. Is provided. In addition, a contact layer 240 is preferably provided. Further, the fifth ferromagnetic layer 210, the second nonmagnetic layer 220, and the sixth ferromagnetic layer 230 are provided adjacent to each other in this order, thereby forming a magnetic tunnel junction (MTJ).

  Preferably, the center of gravity of the fifth ferromagnetic layer 210 is shifted from the center of gravity 12 of the magnetization free region 12 of the first ferromagnetic layer 10 in the xy plane. Now, the direction of this shift is defined as the first direction. Here, the center of gravity indicates a geometric center of gravity, but since each layer has a substantially uniform density, it may be considered to be a center of gravity.

  The fifth ferromagnetic layer 210 and the sixth ferromagnetic layer 230 are made of a ferromagnetic material having magnetic anisotropy in the in-plane direction. The direction of magnetic anisotropy of the fifth ferromagnetic layer 210 is arbitrary in the in-plane direction. On the other hand, the magnetization of the sixth ferromagnetic layer 230 is substantially fixed in one direction. This direction is preferably parallel to the first direction.

  According to this modification, the information stored in the direction of magnetization in the perpendicular direction of the magnetization free region 12 is the surface constituted by the fifth ferromagnetic layer 210, the second nonmagnetic layer 220, and the sixth ferromagnetic layer 230. It can be read by an MTJ having internal magnetization. The principle will be described with reference to FIGS. 19A and 19B. In FIG. 19A, the state of magnetization of each layer in the “0” state is indicated by an arrow, and in FIG. 19B, the state of magnetization in the “1” state is indicated by an arrow. The magnetizations of the first magnetization fixed region 11a, the second magnetization fixed region 11b, and the sixth ferromagnetic layer 230 are depicted as being fixed in the positive z-axis direction, negative direction, and negative y-axis direction, respectively. However, there is arbitraryness between them. Since this optionality is obvious, it is omitted.

  In the “0” state in which the magnetization free region 12 is magnetized downward as shown in FIG. 19A, the magnetization of the fifth ferromagnetic layer 210 is negative in the y-axis due to the leakage magnetic flux generated by the magnetization in the magnetization free region 12 in the downward direction. Turn to the direction. This is because the fifth ferromagnetic layer 210 is arranged below the magnetization free region 12 (in the negative z-axis direction), and the center of gravity of the fifth ferromagnetic layer 210 is in the negative y-axis direction with respect to the magnetization free region 12. This is because they are provided in a shifted manner. As a result, the magnetizations of the fifth ferromagnetic layer 210 and the sixth ferromagnetic layer 230 become parallel, and this MTJ enters a low resistance state. On the other hand, in the “1” state in which the magnetization free region 12 is magnetized upward as shown in FIG. 14B, the magnetization of the fifth ferromagnetic layer 210 is y by the leakage magnetic flux generated by the upward magnetization of the magnetization free region 12. Direct in the positive direction. As a result, the magnetizations of the fifth ferromagnetic layer 210 and the sixth ferromagnetic layer 230 become antiparallel, and this MTJ is in a high resistance state. Thus, the information stored as the magnetization in the perpendicular direction of the magnetization free region 12 is transmitted to the magnetization of the fifth ferromagnetic layer 210 having the in-plane magnetization, and can be read out by the MTJ composed of the in-plane magnetization.

  In general, a high magnetoresistive effect ratio (MR ratio) can be obtained in an MTJ configured by in-plane magnetization. As a result, a large read signal can be obtained.

  19A and 19B, the fifth ferromagnetic layer 210, the second nonmagnetic layer 220, and the sixth ferromagnetic layer 230 are disposed on the lower side (z-axis negative direction) with respect to the first ferromagnetic layer 10. Although depicted as a thing, this position is arbitrary and may be, for example, the upper side. In addition, the first direction, which is the direction of deviation of the center of gravity of the fifth ferromagnetic layer 210 from the center of gravity of the magnetization free region 12, is drawn as a negative y-axis direction in the figure, but this is also arbitrary. And may be in the positive y-axis direction or may contain an x component.

(Fifth modification)
20A to 22B schematically show the structure of a fifth modification of the magnetoresistance effect element according to the present invention. The fifth modification relates to the shape of the first ferromagnetic layer 10.

  In the magnetoresistive effect element according to the present invention, the shape of the first ferromagnetic layer 10 is arbitrary. In FIGS. 1A to 1C, the first ferromagnetic layer 10 is depicted as being rectangular in the xy plane, but FIGS. 20A to 22B show modifications regarding the shape of the first ferromagnetic layer 10. Yes. 20A, 20B, 21A, 21B, and 22B show xy plan views. FIG. 22A shows a perspective view of the first ferromagnetic layer 10 having the shape as shown in FIG. 22B.

  The first ferromagnetic layer 10 may be provided with a notch as shown in FIG. 20A, for example. By providing this notch at the boundary between the first magnetization fixed region 11a and the magnetization free region 12 and at the boundary between the second magnetization fixed region 11b and the magnetization free region 12, the pinning position of the domain wall can be clearly defined.

  Further, the first ferromagnetic layer 10 may be formed so that the central portion is thick as shown in FIG. 20B. The domain wall has the property of moving as narrow as possible in order to lower the energy of the entire system. However, by forming the center part thick as shown in FIG. 20B, the domain wall is less likely to stop at the center part, and a stable binary value is obtained. A state is realized.

  In the first ferromagnetic layer 10, the magnetization fixed region 11 may be formed thicker than the magnetization free region 12 as shown in FIGS. 21A and 21B. FIG. 21A shows an example in which both the first magnetization fixed region 11a and the second magnetization fixed region 11b are formed thick. FIG. 21B shows an example in which only the second magnetization fixed region 11b is formed thick. By forming the magnetization fixed region 11 wider than the magnetization free region 12, it is possible to prevent the domain wall from passing through the magnetization free region 12 and entering the magnetization fixed region 11. This is because the current density decreases in the magnetization fixed region because the width increases.

  The first ferromagnetic layer 10 may be formed in a Y shape as shown in FIGS. 22A and 22B. 22A and 22B, the first ferromagnetic layer 10 has a magnetization free region 12 provided extending in the x direction, and a first magnetization fixed region provided connected to one end (−x side) thereof. 11a and a second magnetization fixed region 11b provided in the same manner connected to one end. That is, the first ferromagnetic layer 10 forms a three-way path. Also in this case, the magnetizations of the first magnetization fixed region 11a and the second magnetization fixed region 11b are fixed at least partially in the vertical direction and in antiparallel directions. In addition, the magnetization of the magnetization free region 12 is either vertical or vertical.

  A writing method when the first ferromagnetic layer 10 has a Y-shape as shown in FIGS. 22A and 22B will be described with reference to FIGS. 23A and 23B. FIG. 23A schematically shows a method of writing “1” from the “0” state, and FIG. 23B schematically shows a method of writing “0” from the “1” state. Now, in the “0” state in which the magnetization free region 12 is magnetized downward as shown in FIG. 23A, a domain wall (DW) is formed at the boundary between the first magnetization fixed region 11 a and the magnetization free region 12. Here, if a current is passed in the direction of the dotted line in FIG. 23A, the domain wall (DW) moves to the side opposite to the end connected to the first magnetization fixed region 11a of the magnetization free region 12 due to the current induced domain wall movement phenomenon. , Transition to the “1” state as shown in FIG. Similarly, in the “1” state in which the magnetization free region 12 is magnetized upward as shown in FIG. 23B, a domain wall (DW) is formed at the boundary between the second magnetization fixed region 11 b and the magnetization free region 12. If a current is passed in the direction of the dotted line in FIG. 23B, the domain wall (DW) moves to the opposite side to the end of the magnetization free region 12 connected to the second magnetization fixed region 11b due to the phenomenon of current induced domain wall movement. , Transition to a “0” state as shown in FIG. 23A. In this way, information can be rewritten.

  When the first ferromagnetic layer 10 is formed in a three-way shape as shown in FIGS. 22A and 22B, writing is performed by extracting the domain wall at the end of the magnetization free region 12. By such a writing process, a more stable writing operation can be realized.

(Other)
Moreover, you may use all the above-mentioned modifications in combination.

  Examples of utilization of the present invention include nonvolatile semiconductor memory devices used in mobile phones, mobile personal computers and PDAs, and microcomputers with built-in nonvolatile memory used in automobiles and the like.

  Although the present invention has been described with reference to several embodiments, these embodiments are merely described for explaining the present invention and should not be referred to in order to limit the content of the claims. This will be apparent to those skilled in the art.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-095757 for which it applied on April 2, 2008, and takes in those the indications of all here.

Claims (12)

A first ferromagnetic layer composed of a ferromagnetic material having perpendicular magnetic anisotropy at least in part;
A second ferromagnetic layer group composed of a ferromagnetic material having perpendicular magnetic anisotropy at least in part,
The first ferromagnetic layer includes a first magnetization fixed region, a second magnetization fixed region, and a magnetization free region,
The second ferromagnetic layer group includes a second ferromagnetic layer, and a first coupling layer provided between the first magnetization fixed region and the second ferromagnetic layer ,
At least a portion of the first magnetization fixed region has a magnetization component fixed in an antiparallel direction with respect to at least a portion of the second magnetization fixed region;
At least a portion of the first magnetization fixed region is magnetically coupled to at least a portion of the second ferromagnetic layer and has a magnetization component fixed in an antiparallel direction with respect to at least a portion of the second ferromagnetic layer. And
And further comprising another ferromagnetic layer group that is magnetically coupled to the second magnetization fixed region at least in part,
The other ferromagnetic layer group includes another ferromagnetic layer, and another coupling layer provided between the second magnetization fixed region and the other ferromagnetic layer,
The product of the saturation magnetization and the film thickness of the second ferromagnetic layer is larger than the product of the saturation magnetization and the film thickness of the first magnetization fixed region, and the saturation magnetization and the film thickness of the other ferromagnetic layer are The magnetoresistive element is smaller in product than a product of saturation magnetization and film thickness of the second magnetization fixed region . A first nonmagnetic layer provided adjacent to the magnetization free region;
A third ferromagnetic layer provided adjacent to the first nonmagnetic layer and on the opposite side of the magnetization free region;
At least a portion of the third ferromagnetic layer has a magnetization fixed in substantially one direction parallel to the magnetization direction of at least a portion of the first ferromagnetic layer.
The magnetoresistive effect element according to claim 1. A fifth ferromagnetic layer magnetically coupled to the first ferromagnetic layer;
A second nonmagnetic layer adjacent to the fifth ferromagnetic layer;
A sixth ferromagnetic layer adjacent to the second nonmagnetic layer on the opposite side of the fifth ferromagnetic layer;
The center of gravity of the fifth ferromagnetic layer is provided to be shifted in a first direction parallel to the film surface with respect to the center of gravity of the magnetization free region,
The fifth ferromagnetic layer has magnetization that can be reversed in a direction parallel to the film surface,
The sixth ferromagnetic layer has a magnetization fixed in a direction substantially parallel to the first direction.
The magnetoresistive effect element according to claim 1. The first magnetization fixed region is connected to one end of the magnetization free region,
The second magnetization fixed region is connected to the other end of the magnetization free region
The magnetoresistive effect element according to claim 1. The first magnetization fixed region and the second magnetization fixed region are connected to the same end portion of the magnetization free region.
The magnetoresistive effect element according to claim 1. At least one of the first magnetization fixed region and the second magnetization fixed region has a planar shape wider than the magnetization free region.
The magnetoresistive effect element according to claim 1. The second ferromagnetic layer group includes a fourth ferromagnetic layer.
The magnetoresistive effect element according to claim 1. The second ferromagnetic layer group includes a second coupling layer.
The magnetoresistive effect element according to claim 1. The second ferromagnetic layer group includes an antiferromagnetic layer.
The magnetoresistive effect element according to claim 1. The first coupling layer is provided adjacent to the lower surface of the first ferromagnetic layer.
The magnetoresistive effect element according to claim 1. The first coupling layer includes Ru
The magnetoresistive effect element according to claim 1. A magnetic random access memory that stores information by the magnetoresistive effect element according to claim 1.

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